Lecture 6 Flashcards
how many nucleotides are in a codon?
three
how many amino acids are there?
20
what is the concept of redundancy?
having multiple codons for one amino acid
what is the reading frame?
it is a way of dividing the nucleotides into sets of three
what is the mediator between mRNA and the protein sequence?
tRNA
how is redundancy managed? (2)
having more than one tRNA for the same amino acid
having tRNA that can base pair with more than one codon
where can ribosomes be found? (2)
on endoplasmic reticulum
in cytosol
what are ways of ensuring accuracy when matching with the genetic code? (3)
aminoacyl-tRNA synthetase
base pairing
aminoacyl tRNA synthetase correcting by hydrolytic editing
how is transfer RNA recognized? (3)
identifying the anticodon of the tRNA
recognizing the sequence on the acceptor’s arm
reading nucleotides on other positions on tRNA
How does the energy stored in the P site’s covalent bond between an amino acid and tRNA contribute to the energetically favourable peptide synthesis process?
makes peptide synthesis
energetically favourable
what is a ribozyme?
a ribosome with catalytic properties
what is the function of EF-Tu (EF1 in euk.)?
Checks
aminoacyl tRNA
what happens to EF-Tu if the base pairing is not correct?
not released
what happens to peptide bonds if the base pairing is not correct?
they will not form
what happens if the base pairing is correct? (2)
GTP is hydrolyzed
ET-Tu released
what is the purpose of the slight delay before the formation of p.p
bond?
allows one last check for accurate base-pairing
what is the function of EF-G (EF2 in euk.)
helps the ribosome to move the mRNA
forward one codon at a time
helps speed up elongation of the
polypeptide chain
Can ribosomes perform protein synthesis without the aid of elongation factors?
Yes, but…..slower and inefficient
what is the role of elongation factors? (2)
improving speed and efficiency
error checking
what is elongation mediated by?
GTP hydrolysis and release of EF-Tu & EF-G
what does Polycistronic mean?
a type of mRNA molecule that carries the genetic information for multiple proteins
what is the role of Shine-Dalgarno sequences during translation initiation in prokaryotes?
bind directly to the small ribosomal subunit’s mRNA-binding site.
What is the significance of initiation factors (IFs) towards ribosomes during translation initiation?
IFs help position the small ribosomal subunit to the initiating AUG codon on mRNA
During translation initiation, when does the large ribosomal subunit bind to the complex?
After initiation factors have dissociated
What is the typical spacing of nucleotides observed during protein synthesis?
Every 80 nucleotides
Which molecule binds to the initiator codon (AUG) during translation initiation?
Methionine tRNA
what is the function of the human translation release factor?
terminating translation by recognizing stop codons
Which are examples of molecular chaperones involved in protein folding?
Hsp60 and Hsp70
what is the function of chaperone proteins?
helps proteins fold
Which types of post-translational modifications are commonly observed in proteins?
Phosphorylation and glycosylation
What is the purpose of covalent modifications in proteins?
To make the protein active or to recruit it to the correct membrane or organelle
What is the cellular structure responsible for degrading proteins tagged with ubiquitin?
Proteasome
What cellular process targets proteins for degradation when they are tagged with ubiquitin?
Proteasomal degradation
Which enzymes are responsible for degrading proteins within the proteasome?
Proteases
what do many antibiotics act on?
ribosomes
